Testing system



P. G. EDWARDS July 4, 1933.

TESTING SYSTEM Filed Fb. 21,1930

INVENTOR GZ'dwwmds ATTORNEY Patented July 4, 1933 UltlTE SATS PATENT GFFEQE PAUL G. EDNART JS, OF BLOOMFIELD, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH. COMPANY, A GORPORATIOIT OF NEW YORK TESTING SYSTEM Application f led February 21, 1930, Serial No. 430,358,

This invention relates to testing systems. More particularlythis invention relates to arrangements for locating a fault in a conductor.

When making Varley loop measurements for the location of a fault in a conductor, galvanometer fluctuations which may be pro duced by potentials induced from telegraph circuits, particularly those of the simplex and composite variety, and from other circuits, are often very troublesome, especially if the fault resistance is high. All of these extraneous effects greatlyaifect the speed as well as the accuracy required in the location of the fault.

One of the objects of this invention is to provide, in addition to the apparatus employed for making Varley loop measurements, means for neutralizing fluctuations in the alvanometer caused b forei n induced b 23 7 1 or other extraneous currents.

Another object of this invention resides in the provision of an arrangement such that extraneous potentials or induced currents 1 tending to cause galvanometer fluctuation I of illustration.

The drawing shows an arrangement for substantially neutralizing the effects of extraneous voltages often known as ground po tentials. The reference characters A and B represent equal elements of resistance one end of each of which is connected to the other and to ground through a resistance P and a source of direct current which may be a battery designated D. The other ends of the I resistances A and B areinterconnected by a galvanometer- G which may be of'any well known type. A faulty wire is designated V and one end of this wire is connected to the junction of the galvanometer G and the resistance B through a rheostat R. A good conductor designated l/V is connected to the junction of the galvano-meter G and the re sistance A. The other ends of the conductors l/V and VV are connected to each other. The elements just described represent those which are frequently used for making Varley loop measurements to determine the location of a fault which may be present in the conductor Nb, some point of which is grounded through resistance shown by dotted lines and designated F.

When the fault is at the extreme end of the conductor N then both conductors VVD and will be equally affected by induced voltages or other extraneous effects, and the pointer of the galvanometer G will not be fluctuated onaccount of these effects. Then the fault does not occur at the extreme end of a conductor, a fault seldom occurring at that point, then the effective voltages resulting from extraneous potentials will differently affect conductors Q and W and consequently the pointer of the galvanorneter will be fluctuated. In that event, it will be diflicult, if not impossible, to make an accurate determination of the distance to the fault.

In accordance with this invention, all of the resistance of a potentiometer S is bridged across the galvanometer G. A neutralizing conductor Vi] is connected in series with a condenser C to the moving contact or element of thepotentiometer S. The junction of the conductor W and the condenser C is connected to the junction of the resistances A and B through a resistance Q. With this arrangement the resistance Q represents a low impedance for direct current as compared with the insulation resistance of the con denser C. Yet, resistance Q interposes a high impedance for alternating currents. The condenser C is of large capacity and presents low impedance for alternating currents, yet its impedance is practically infinite for direct current. With this arrangement, any leakage current from battery D to conductor flows through the resistance Q, rather than through the relatively high resistances presented by the arms, A and B of the bridge and the upper and lower portions of potentiometer S, respectively, and condenser C, and therefore such current will not affect the galvanometer Gr. Only so much of the current from battery I) as flows over the good and bad conductors W and V respectively, will be effective in causing the moving element of the galvanometer to become deflected.

In a general way it will be evident that potentials induced in the conductor Q will be greater than those induced in the conductor Vb because the latter conductor will be grounded through a resistance F at a point somewhat distant from its extreme end. Those potentials induced in conductors W and .V will therefore differently affect gal- Vanometer G, and the difference between these potentials will be the one it will be necessary to neutralize. V The neutralizing conductor VV should be selected so that potentials induced therein will be approximately the same in magnitude and phase as those in duced in the conductor when \V is free. The required amount of neutralization may be obtained by properly setting the potentiometer S. WVhen the proper setting obtaincd, the potentials impressed on the two sides of the galyanometer will be equal and opposite to those caused by conductors IV and Q, and the net Voltage from the inducing sources will be zero. It will be apparent that the neutralizing conductor IV should preferably be in the same quad as both con ductors and V1,, and moreover, it should have an insulation resistance to ground of the same order to magnitude as that of the good conductor The condenser C has a sutliciently low impedance so as not to appreciably affect the phase angle or magnitude of the neutralizing current.

It is to be noted that a pair of conductors may be substituted for the one designated IV and one end of one of these may be connected to an end of the other and to condenser C. The two conductors will then be open-circuited at their other ends, as is the conductor W shown in the drawing. The pair of conductors should have. an insulation resistance to ground comparable with that of the conductor Q.

In determining the location of a fault in conductor V the bridge will be balanced as closely as possible in the usual manner by the adjustment of the resistance R. Then the potentiometer S will be adjusted until the galvanometer indicates a minimum of fluctuation. Under ordinary circumstances the pointer of the galvanometer will be practically stationary. The position of the movable arm of thepotentiometer will depend upon the location of the fault and the relative insulation resistances of the conductors involved. It has been found that when the fault is at the distant end of the conductor V it will be necessary to set the potentiometer at its midpoint. hen the fault is very close to the rheostat R it will be necessary to move the variable element of the potentiometer to its lower terminal. In general, the potentiometer will require setting at an intermediate position for any other location of the fault. The actual location is made in the usual manner.

In an arrangement actually constructed in accordance with the layout of the drawing,

the resistance G was 100,000 ohms, the total resistance of the potentiometer was 4000 ohms, and the condenser Chad a capacity of 20 microfarads. Fluctuation of the galvanometer was neutralized to a very high degree.

\Vhile this invention has been shown in one particular arrangement merely for the purpose of illustration, it will be understood that the features of this invention maybe applied to other and widely varied organizations without eparting from the spirit of the invention and the scope of the appended claims.

lVhat is claimed is:

1. The combination of apparatus includiug galvanometer for making Varley loop measurements, and means capacitively coupled to the galyanometer supplying currents for neutralizing the effects of extraneous potentials which fluctuate the pointer of the galvanometer.

2. The combination of a \Vheatstone bridge circuit adapted to make Varley loop measurements and including a galvanometer, a potentiometer in shunt across one diagonal of said VVheatstone bridge circuit, and means for transmitting currents to the potentiometer for neutralizing the effect on the VVheatstone bridge circuit of extraneous interfering potentials.

3. The combination of a Wheatstonc bridge circuit, a potentiometer in shunt with one diagonal of the bridge circuit. and means for transmitting currents to the potentiometer for neutralizing the effect on the VVheatston ridge circuit of extraneous interfering potentials.

4. The combination of a. \Vheatstone bridge'circuit, one of the arms of which includes av conductor to be tested, and means coupled to one diagonal of said circuit to neu tralize the effects of potentials superimposzd on said conductor.

5. The combination of a \Vheatstone bridge circuit, a potentiometer connected as a. diagonal of said circuit, an open-ended conductor connected to the adjustable arm of said potentiometer, and means to bypass leakage currents over said conductor from Said circuit.

6. The combination of a VVheatstone bridge circuit, an open-ended conductor connccted to said circuit, and means to substantiallysupprcss the efi'ects of leakage current over said conductor from said circuit.

7. The combination of a conductor, testing apparatus for locating a fault on the conduc tor, means for neutralizing the effects upon said apparatus of currents induced in said conductor, and means for substantially eliminating the effect upon said apparatus of leakage current through said conductor.

8. The method of locating a fault in a conductor with lVheatstone brid e apparatus, which consists in making the ordinary Varley loop measurements and supplying currents to the lVheatstone bridge apparatus from a parallel conductor which is open ended for neutralizing the effect of ground potentials on these measurements.

9. The method of locating a fault in a conductor with Varley loop apparatus which includes'a galvanometer, which consists in receiving over a parallel opened-ended conductor extraneous potentials which interfere with the measurements and impressing these potentials on the galvanometer for neutralizing the effects of these potentials.

10. The combination of testing apparatus including a galvanometer'to locate a fault on a conductor, and means including a parallel open-ended conductor which supplies current to neutralize the eiiects of extraneous induced potentials impressed upon the galvanometer of said apparatus.

11. The combination of a potentiometer, indicating means electrically coupled to said potentiometer, and an open-ended, current carrying conductor capacitively connected to the movable arm of the potentiometer, said conductor being exposed to extraneous potentials and supplying currents for neutralizing the etlccts on the indicating means of these extraneous potentials.

12. The combination of apparatus for malring Varley loop measurements and including a galvanometer, a potentiometer bridging the galvanometer, and a wire capacitively connected to the movable arm of the potentiometer, said wire being exposed to extraneous potentials and supplying the currents required for neutralizing the effects of these extraneous potentials which may fluctuate the pointer of the galvanometer.

13. The combination of a measuring instrument forming a part of a testing system, a resistance shunting said instrument, an open-ended wire exposed to extraneous voltages and carrying currents produced by these voltages, and a condenser interconnectv ing that wire with some point on said resistance, the current carried by said wire neutralizing the effects of these extraneous potentials which may disturb the measuring instrument.

14. he combination of apparatus including a galvanoineter for testing purposes, a loop embodying conductors to be tested and connected in series with the galvanometer, a potentiometer shunting said galvanometer, and a wire one end of which is capacitively connected to the movable arm of said potentiometer, said wire being exposed to extraneous potentials and supplying currents for neutralizing the effects of these extraneous potentials which may fluctuate the i pointer ot' the galvanometer.

15. The combination of testing apparatus including a galvanometer, a good wire, a bad wire in series with the good wire and the galvanometer, a potentiometer shunting the galvanometer, a neutralizing wire, and a condenser connecting one end of said neutralizing wire to the movable arm of the potentiometer, the other end of the neutralizing wire remaining open, said neutralizing wire being exposed to extraneous potentials and supplying currents to overcome the effects of these extraneous potentials which may fluctuate the pointer of the galvanometer.

16. The combination of two equal resistances having a common unction, a galvanometer connected between the other ends of said resistances, said resistances and said galvanometer forming part of a testing sys tem, a first conductor one end of which is connected to one terminal of the galvanometer, a second conductor one end of which is connected to the other terminal of the galvanometer, the other ends of said first and second conductors having a common junction, a potentiometer shunting the galvanometer, a third conductor, and a condenser interconnecting one end of the third conductor with the movable arm of the potentiometer, the third conductor being exposed 'to extraneous potentials and supplying currents for neutralizing the effects of these extraneous potentials which may fluctuate the pointer of the galvanometer.

17. The combination of two equal resistances which have a common junction, a galvanometer interconnecting the other ends of said resistances, said resistances and said galvanometer forming part of a testing system, a first conductor one end of which is connected to one terminal of the galvanometer, a second conductor one end of which is connected to the other terminal of the galvanometer, the distant ends of said first and second conductors having a common junction, a potentiometer shunting the galvanometer, a third conductor, a condenser interconnecting one end of the third conductor with the movable arm of the potentiometer, and a third resistance interconnecting the same end of the third conductor with the junction of said first and second resistances, the third conductor being exposed to extraneous potentials and supplying currents for neutralizing the eilects of these extraneous potentials which may fluctuate the pointer of the galvanometer.

18. The combination of two equal resistances which have a common junction, a galvanometer interconnecting the other ends of said resistances, a first conductor one end of which is connected to one terminal of the galvanometer, a second conductor one end of which is connected to the other terminal of the galvanometer, the distant ends of said first and second conductors having a common junction, a potentiometer shunting the galvanometer, a third conductor, a condenser interconnecting one end of the third conductor with the movable arm of the potentiometer, a third resistance interconnecting the same end of the third conduct-or with the junction of said first and second resist ances, and a grounded battery connected to the junction of said equal resistances, the third conductor being exposed to extraneous potentials and supplying currents for neutralizing the eilects of these extraneous potentials which may fluctuate the pointer of the galvanometer.

19. The combination of two equal resistances which have a common junction, a galvanometer connected to the other terminals of said resistances, a good conductor one end of which is connected to one terminal of the galvanometer, a bad conductor, a rheostat interconnecting one end of the bad conductor with the other terminal of the galvanometer, the distant ends of the good and bad conductors having a common junction, a potentiometer shunting the galvanometer, a neutralizing conductor, a condenser interconnecting one end of the neutralizing conductor with the movable arm of the potentiometer, a third resistance interconnecting the same end of the neutralizing conductor with the junction of the two equal resistances, and a grounded battery connected to the junction of said two equal resistances, the neutralizing conductor being exposed to extraneous potentials and supplying currents for neutralizing the efl'ects of these extraneous potentials which may fluctuate the pointer of the galvanometer.

20. The combination of a VVheatstone bridge circuit, a potentiometer connected as a diagonal of said circuit, and an open-ended conductor connected to the movable arm of said potentiometer, said conductor being exposed to extraneous potentials and supplying currents for neutralizing the effects of these extraneous potentials which may reach the 'heatstone bridge circuit.

21. The method of locating a fault with apparatus including a galvanometer for making Varley loop measurements, which includes exposing an open-ended conductor to undesired effects and simultaneously sending through the galvanometer currents derived from the open-ended conductor to overcome these undesired etfeets'on the galvanometer.

In testimony whereof, I have signed my name to this specification this 20th day of February, 1930,

PAUL G. EDWARDS. 

